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The only trouble I see with going to the 8085, is the loss of the status byte. It can be partially recreated by decoding the state lines, which have to be done anyway to differentiate I/O vs Memory access. But a "Stack" and "Inte" signal can not be gotten.
The main purpose of this board was to be compatible with the front panels of the ALTAIR and IMSAI. Does the group want to drop that *full* compatibility and go with an 8085 board? I put it to a vote. The 8085 can function with limited functionality with the front panels. Here's a break down of the front panel and what's loss. + indicates signal can be produced STATUS BUS +MEMR +INP +M1 (fetch) +OUT +/WO +HLTA -STACK (no more indication of STACK operations, no big loss) +INTA CONTROL BUS -INTE (no indication of Interrupts enabled, no big loss either) +HLDA -WAIT (no indication of a WAIT mode... is that right? or am I missing something in the data sheet?) Further, the RUN/STOP function will not stop on a M1 (Fetch cycle). this will cause erratic behavior of the Examine/Next functions. Work around is to single step to an M1 function then use "Examine". This might be the biggest down fall of the 8085 CPU, but not the end of the world since the Z80 had the same problem with the old front panels, and many didn't care about it. I can't say we are losing much, but everyone has their own opinions of what's important. I put it to a vote and/or discussion. Cheers, Josh From: rich...@verizon.net Subject: Re: [N8VEM-S100:5635] Re: 8080a board Date: Thu, 20 Nov 2014 10:33:20 -0500 To: n8vem...@googlegroups.com All good ideas, especially the 8085 and the sense switch input. I wish the msdos board had a sense switch input. Sent from my iPhone
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